i was wondering if rainwater would be idea for use in aquariums. specifically a planted aquarium. iv been thinking about this as a solution to reduce the amount of ground water that i use in the aquarium which is about 10 to 15 gallons per week and another befit i would enjoy is having water with a lower ph, currently its somewhere around 8.4. i figure it would get contaminated if its run off from the gutters on my roof which will have touched dead leafs, moss, chemicals from building material, bird poo etc. so im trying to find a way to collect it with out it touching the roof. also before seriously considering this i would be measuring the ph of the rain water that collects around my house for a period of time and contacting someone to find out if there is already a high level of pollutants in the rainwater. if anyone has information has to the likely hood of there being high pollutants in rainwater that is not acceptable for use in an aquarium please tell me and also if anyone has any idea how i would go about collecting the rainwater please share your ideas.